Growth of a layer of W6Co7 phase in systems with participation of phases containing cobalt

Abstract

Growth kinetics for a layer of W 6 Co 7 at the interfaces tungsten-cobalt and tungsten-melts based on copper and tin containing cobalt at 1200°C are studied. It is established that rate constant for growth of this layer in the system with participation of tin (k Sn ) is much greater than in the system with copper (k Cu ). Dependences are determined for these constants on cobalt activity in the melt (a Co ): k Cu (m 2 /sec) = = 1.72 ⋅ 10 -15 (a Co − 0.221) + 2.99 ⋅ 10 -14 (a Co − 0.221) 2 ; k Sn (m 2 /sec) = 1.8 ⋅ 10 -14 (a Co − 0.221) + + 9.077 ⋅ 10 -12 (a Co − 0.221) 3 .

X-ray analysis of the phase composition of liquid-phase interaction products of W, Co, and Sn powders

“…Moreover, the production of dense compacts by liquid-phase sintering at relatively low temperatures is very promising. The kinetics and mechanism of liquid-phase sintering of tungsten were studied in [1][2][3][4][5][6].This paper deals with x-ray diffraction analysis of composites compacted and sintered from W, Co, and Sn powders for 1 h at 1200°C in hydrogen followed by cooling in a furnace. The composites were as follows, wt.%: 90 W-7 Co-3 Sn, 90 W-3 Co-7 Sn, and 90 W-2 Co-8 Sn.…”

“…Moreover, the production of dense compacts by liquid-phase sintering at relatively low temperatures is very promising. The kinetics and mechanism of liquid-phase sintering of tungsten were studied in [1][2][3][4][5][6].…”

Effect of interaction between the structural components of W-Co-Sn pseudo-alloys on the kinetics of their compaction during liquid-phase sintering

“…Under these conditions reaction at the tungsten − cobalt contacts may be ignored since even at 1200°C the growth constant for intermediate intermetallic W 6 Co 7 in the contact zone of solid tungsten and cobalt is about 7.36 × × 10 −16 m 2 ⋅ sec [5].…”

“…It is well known [9] that in the W − Co − Sn system at a certain temperature and a certain cobalt content in the Co − Sn melt three-phase equilibrium W + Co (Co+Sn) ↔ W 6 Co 7 is achieved. According to precise data [5], at 1200°C it is achieved with a content in the melt of about 25 mass% Co. In the specimens tested with 3, 3.5, 4, 5, and 7 mass% Co at 1200°C a liquid phase forms containing cobalt that exceeds 25 mass%.…”